In the U.S. Pat. No. 3,902,374 assigned to the same assignee as the present invention, there is disclosed a captured type two-axis gyroscope which has a Saturn-Shaped rotor disposed within an evacuated housing. In that invention, an electrostatic rotor suspension system is utilized to provide frictionless rotor spin bearing. Those electrostatic forces associated with suspension are applied to the spherical portion of the rotor and pass essentially through the center of the rotor and thus, by design, produce no torques on the rotor. Those electrostatic forces producing angular capture are applied to the ring structure portion of the rotor by capture electrodes mounted on a cup-shaped support member which has limited rotational movement about two perpendicular axes that are parallel to the gyroscope precession axis. A pair of vibrating beam force transducers are connected between the support member and the housing to sense the reaction torque exerted by the capture system so that the reaction torque exerted by the capture system provides two axis rate output signals.
The approach of the present invention is through the use of the captured-type rotor rather than a free rotor gyro for two important reasons. First, every free gyro with extremely wide angle capabilities requires a wide angle pickoff capable of precise and fine angular resolution. Most transducers which have been developed in this area have been complex, cumbersome and expensive. The second reason for avoiding the free gyroscope approach is that the restraints on free gyroscopes generally change with angular position of the rotor. In the case of electrostatic gyroscopes torques appear on the rotor as a result of deviation from perfect rotor sphericity. If the gyro has a very limited angular freedom it is possible to achieve very good performance through cancellation of restraints throughout the suspension system. This is impossible over wide angles. Therefore, the free gyro requires better geometrical control and also more extensive testing than a captured gyro.